Optimizing forest nursery production
For forest nurseries it’s quite simple to obtain all the benefits from managing resources on demand, if you (1) focus on the quality, (2) stick to one simple methodology with precision, and (3) realize that you don’t need to grow the plantlets unnecessarily big.
Allow me to illustrate with a successful trial of both spruce and birch. The trial compared different fertilizer regimes and was performed under commercial-like conditions, in which a complete liquid fertilizer was supplied via the irrigation system to the peat soil in which the tree seedlings grew (see table for details).
In the trial three fertilizer supply methods were compared:
A conventional linear supply. Approximately constant pre-determined amounts of nutrients were supplied over time, in the same manner and amounts as in conventional commercial production in the area.
Demand-driven supply, intended to sustain maximal growth
The nutrient supply followed the growth pattern of the plant, and dosage increased with the growth rate of the plant. The total amount of nutrients supplied by the end of the season was less than 50 % of the conventional supply.
Demand-driven supply at growth limiting rate
The nutrient supply followed the same pattern as in previous method, but at a limited rate that ensured limitation in the nitrogen supply. This meant a nutrient supply over the season that was about 50 % of the previous method (no. 2). However, by the end of the season a few larger nitrogen recovery doses were given to improve the nutrient status in the tree right before harvest. This meant that the total amount of nutrients supplied was almost as high as in method no. 2.
The results were very clear. Method no. 1 and 2 had similar result. The trees from method no. 1 were marginally taller, with a slightly larger biomass. The trees from method no. 3 reached about 2/3 of both height and biomass of those in method no. 1. All trees looked healthy by the end of the season, and all were ready for plantation in bare ground.
Another interesting comparative feature was the rootsize relative to the whole tree. Method no. 1 gave the smallest relative root size (by far), and the method no. 3 the largest (by far). Relative root-size is an incredibly important trait for boosting growth and withstanding stress after replantation in the bare ground.
Nutrient status in the plant is also another important factor when the plantlet is planted in the bare ground, as it needs immediate access to nutrients to grow. Due to the large fertilizer additions by the end of the season in method no. 3, the trees from that treatment had the best nutrient status by far.
And let’s not forget the environment. Method no. 1 led to the highest nutrient losses through leaching without comparison.
So, in summary, the demand-driven supply methods provided healthier trees with larger root systems, with considerably less fertilizers, and considerably smaller nutrient losses. And depending on version of the demanddriven supply, i.e. aiming for maximum growth or limited supply, the trees were either grown to virtually the same size as the conventional with the half amount of fertilizers, or the trees were successfully charged with a good nutrient storage before planting in the bare ground. Also, the minor differences between method 1 and 2, can easily be mended with minor adjustments in the standard demand-driven method.
To implement this method in forest nursery production is reasonably easy. Simply use a complete fertilizer that reflects the ratios in the table that I have provided, and frequently supply it in doses matching the growth rate of the plant, that is: increase the doses with the same percentage as the seedlings increase in biomass for each time unit. Remember to keep the nutrient supply all the way to transplantation in order to enable top nutrient status in the plants.
If you implement this methodology you can attain the following benefits in your production: Considerably lowered fertilizer consumption, More vital plants, Stronger root system, Nutrient storage in the plant, Energy storage in plant, Virtually remove nutrient leaching from nursery production.
The main take-away from my message is that it’s simple, it’s worthwhile and it’s profitable.
Amount of nutrients in the liquid fertilizer used in the trial. The ratio between ammonium and nitrate is 40:60. It is a commercial fertilizer that is based on the discoveries behind demand-driven fertilization.